1 / 40

QCD and Heavy Ions

CERN-DESY Workshop on HERA and the LHC, March 2004. QCD and Heavy Ions. D. Kharzeev BNL. Outline. QCD of strong color fields: parton saturation and Color Glass Condensate CGC and Quark-Gluon Plasma Manifestations of CGC at RHIC:. hadron multiplicities

sybil
Télécharger la présentation

QCD and Heavy Ions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CERN-DESY Workshop on HERA and the LHC, March 2004 QCD and Heavy Ions D. Kharzeev BNL

  2. Outline • QCD of strong color fields: parton saturation and Color Glass Condensate • CGC and Quark-Gluon Plasma • Manifestations of CGC at RHIC: • hadron multiplicities • high pT suppression at forward rapidity • Future tests: RHIC, LHC, eRHIC

  3. QCD and the classical limit QCD = Quark Model + Gauge Invariance For , .i Classical dynamics applies when the action is large: => Need weak coupling and strong fields

  4. Asymptotic freedom and the classical limit of QCD Classical limit S>>1 requires weak coupling and strong fields; Large distances: strong fields but large coupling… Is there a place for classical methods?

  5. Parton saturation and the classical limit of QCD At small Bjorken x, hard processes develop over .large longitudinal distances All partons contribute coherently => at sufficiently small x and/or .large A strong fields, weak coupling!

  6. The phase diagram of high energy QCD … no numbers yet, but they will follow

  7. From CGC to Quark Gluon Plasma L. McLerran, T. Ludlam, Physics Today, October 2003

  8. CGC and total multiplicities in Au-Au CGC predicts very simple dependence of multiplicity .on atomic number A / Npart: Almost like in “wounded nucleon” and string-based models; Agrees unexpectedly well with “soft + hard” parameterizations

  9. Parton interactions at RHIC .are coherent ! dNch/dh @ h=0 vs Energy

  10. Centrality dependence of hadron multiplicity

  11. Centrality dependence at different energies

  12. _ pp Midrapidity charged particle production Au+Au 200 GeV |h|<1 130 GeV Preliminary 19.6 GeV Collision scaling does NOT disappear at low energy. Problem for naïve “minijet” based models. M. Baker, PHOBOS

  13. Initial state parton saturation? QM2002: nucl-ex/0212009 200 GeV 130 GeV Preliminary 19.6 GeV Kharzeev, Levin, Nardi, hep-ph/0111315 l~0.25 from fits to HERA data: xG(x)~x-l Describes energy dependence correctly!

  14. Parton Saturation Describes Au + Au Color Glass Condensate describes the Au-Au data Kharzeev & Levin, Phys. Lett. B523 (2001) 79 PHOBOS Coll., R. Noucier Au + Au at 130 GeV • We need a simpler system such as d + Au in order to understand a complex system Au + Au • The results of d+Au are crucial for testing the saturation approach

  15. D-Au multiplicities Data from BRAHMS and PHOBOS Collaborations

  16. The discovery of high pT suppression at RHIC

  17. What happens at higher transverse momenta? PHENIX and STAR extend measurements to ~ 10 GeV

  18. Centrality Dependence vs pT Phobos Phobos

  19. Is this the jet quenching in QGP? Very likely; .but could there be alternative explanations? (2002)lternative Bjorken; Gyulassy, Wang; Baier, Dokshitzer, Mueller, Peigne, Schiff; Wiedemann, Salgado; Vitev, Levai, … DK, Levin, McLerran hep-ph/0210332 Yes, possibly: 1) Small x evolution leads to .the modification of gluon propagators - “anomalous dimension”: 2) Qs is the only relevant dimensionful parameter in the CGC; .thus everything scales in the ratio Tthe A-dependence is changed => Npart scaling! 3) Since

  20. D-Au collisions: suppression or enhancement?

  21. RdAu vs pT Phobos Central Au+Au

  22. p+p vs. d+Au No “data manipulation” D. Hardtke, STAR Coll. • Azimuthal correlations are qualitatively consistent • Quantitative evaluation will constrain • Nuclear kT from initial state multiple scattering • Shadowing • Models that predict “monojets” due to initial state effects ruled out

  23. Conclusion:high pT suppression is a final-state effect Can one prove that it is due to a radiative jet energy loss In the Quark-Gluon Plasma? Quite likely: one possibility is to use the heavy quarks Yu.Dokshitzer, DK ‘01 Radiation off heavy quarks is suppressed (“dead cone”) => less quenching On the other hand, D mesons have about the same size as .pions and kaons, and so in the hadron absorption scenario .the suppression should be the same

  24. However, the arguments for the CGC-caused,suppression should hold for sufficiently small x; Does this happen at RHIC? Study the forward rapidity region: Moving to y=+4 from y=0 increases the saturation scale .by factor of three

  25. Expectations for RdAu at large rapidity Agreement on the presence of suppression due to the quantum Small x evolution in the CGC picture: DK, E. Levin and L. McLerran, hep-ph/0210332; R. Baier, A. Kovner, U. Wiedemann, hep-ph/0305265 v2 DK, Yu.Kovchegov and K. Tuchin, hep-ph/0307037 v2 J. Albacete, N. Armesto, A. Kovner, C. Salgado, U. Wiedemann, hep-ph/0307179; Agreement on the presence of Cronin effect in the classical ,approach and in the multiple scattering picture: L.McLerran and R.Venugopalan; Yu.Kovchegov and A.H.Mueller; J. Jalilian-Marian; A. Dumitru; F. Gelis;… X.N.Wang; M. Gyulassy; I. Vitev;…

  26. Model predictions D. Kharzeev, Yu. Kovchegov and K. Tuchin, hep-ph/0307037 I. Vitev nucl-th/0302002 v2 CGC at y=0 Y=0 As y grows Y=3 Y=-3 Very high energy R. Debbe, BRAHMS Coll., Talk at DNP Meeting, Tucson, November 2003

  27. d-Au Nuclear Modification factor at  ~3.2 RdAu compares the yield of negative particlesproduced in dAu to the scaled number of particles with same sign in p-p The scale is the number of binary collisions: Ncoll=7.2 (minimum biased) PRL 91 072305 (2003) BRAHMS preliminary R. Debbe, BRAHMS Collaboration, Talk at the DNP Meeting, Tucson, November 2003

  28. RdAu at different rapidities Number of binary collisions in minimum biased events is estimated: Ncoll = 7.2±0.3 Statistical errors dominant over the systematic ones at =2 and 3 Systematic error (not shown) ~15% The values for =0 were published in: PRL 91 072305 (2003) All ratios extracted from minimum biased data samples R.Debbe, BRAHMS, QM’04

  29. Centrality dependence All numerators and denominator are scaled by the appropriate estimated number of binary collisions (HIJING + BRAHMSGEANT) The ratios are corrected for trigger inefficiency. All other corrections (acceptance, tracking efficiency.. ) cancel out. R.Debbe, BRAHMS, QM’04

  30. Discussion BRAHMS has measured a clear modification of the Cronin peak as we detect charged particles at pseudo-rapidities ranging from 0 to 3. We also found that particle yields at all values of pT are more suppressed in central events at high rapidity. Both results are consistent with a description of the Au wave function evolving in ln(1/x) (rapidity) into a saturated non-linear medium.

  31. d Au Centrality Dependence of Particle Production @Fwd/Bwd Directions • Stopped hadrons • Mesons + Baryons • Light mesons • Pions + Kaons • Heavy flavors • Charm + Beauty Ming Liu, PHENIX, QM’04

  32. PhenixPreliminary Au d Stopped Hadrons!

  33. PhenixPreliminary Au d Stopped Hadrons!

  34. PhenixPreliminary Cronin effect & anti-shadowing? d Shadowing? Au Stopped Hadrons!

  35. RCP(y): Muons from Light Meson Decays PhenixPreliminary RCP

  36. d+Au RCP at forward rapidities • Au-Side RCP shows almost no variation with centrality • d-side is interesting: more central is more suppressed RCP L.Barnby, STAR, QM’04 PT [GeV/c]

  37. d Au spectra at (not so) forward rapidity P. Steinberg, PHOBOS, QM’04

  38. Rapidity dependence of RdAu

  39. Phase diagram of high energy QCD

  40. Summary Recent results from RHIC indicate strong non-linear effects at small x Combined with observations at HERA, and supplemented by further tests, these results can lead to the discovery of parton saturation in the Color Glass Condensate Major implications for future programs at RHIC, the LHC, and eRHIC

More Related